1. Field of the Invention
This invention relates to a method for balancing the sensitivity of two channels comprising intermittently-appearing pulse waves.
More particularly, the invention relates to a method of belancing the sensitivity of two channels comprising intermittently-appearing pulse waves, such as the signals generated by respective sensors in a detecting pair which is used in the so-called differential detection of flaws in materials.
2. Description of the Prior Art
In nondestructive testing apparatus such as a magnetic flaw detector or an ultrasonic flaw detector, the principle generally employed is that of differential flaw detection in which a pair of detecting means are caused to scan the same part of the test material at a suitable time interval and the output pulse signals generated by these two detecting means are differentially amplified to improve the detection sensitivity of the apparatus. To accomplish the desired object with such differential detection, the peak values of the flaw signals, i.e. the pulse waves corresponding to any single flaw in the test material, must be identical. While the above conditions are met when the two detecting means have the same sensitivity, it is practically impossible to manufacture two detecting means having exactly the same sensitivity. For this purpose, it is conventional practice to adjust the gains of the preamplifiers provided in the instrument to which these detecting means are directly connected so as to compensate for the difference existing in sensitivity between the two detecting means. This sensitivity compensation is carried out as follows. Thus, a control reference standard which is identical in material and shape with the material to be tested and which has been artificially given a multiplicity of standardized flaws is scanned with the aforementioned two detecting means and the necessary sensitivity compensation is accomplished by the use of the two pulse output signals of the detecting means. However, because the flaw signals corresponding to the flaws on the control reference standard appear only intermittently, the output of the preamplifier is difficult to monitor and, therefore, there are experienced such disadvantages as an inacurrate sensitivity compensation and the prolonged time required for adjustments for obtaining the necessary compensation.
This invention has been accomplished to obviate the foregoing disadvantages. Thus, the invention has as its object to provide means for balancing the levels of two pulse signals, which can be utilized for the compensation for sensitivity differences as noted above, which means comprises causing the peak values of pulse waves in the pulse signals to be held by a sample and hold circuit for an appropriate period of time and, during that time, causing the gain of a variable gain amplifier to be automatically adjusted. This invention will hereinafter be described in detail, reference being had to the accompanying drawing.